With the multi-functionalized, miniaturized and high-performance development of electronic products, the PCB is required to be developed with a higher level, a higher density and higher signal integrity. As such, to have the higher level and higher density, it requires that the PCB should be drilled in very high accuracy. Further, to have the higher signal integrity, it is necessary to reduce sources of signal noise as little as possible.
Currently, the signal integrity, especially, the integrity of high-frequency (HF) signal, is improved by back-drilling the PCB. The back-drilling removes extra metal from a metal hole in the PCB so as to reduce signal reflection caused by the extra metal and thus reduce the signal noise. In order to remove extra metal from the metal hole, a back-drilled hole must have an aperture greater than an outer diameter of the metal hole in the PCB. While removing the extra metal from the metal hole, it is further necessary to prevent damage to metal patterns around the metal hole for transmitting signal.
In related technologies, an alignment between the back-drilled hole and the metal hole in the PCB is detected by a way of slicing. In this way, the PCB under the detection may be scrapped, and the detecting cost is relatively high.